Electric blanket control



Dec. 21, 1948.

H. W. A. CHALBERG ELECTRIC BLANKET common Fiied Jan. 9, 1946 .Invntor: v Harry'WAChalberg,

His Attorney.

Patented Dec. 21, 1948 I Y., assrntr to en ral Electric company; a "corplira ion or New York Application-January 9, 19 16,- Sei-ialNo.639,993

;E In carrying out this invention in'one wt hereofjfa grid-controlled half-wave rectifier lt alve 15 provided to control a suitable control circuit ,ror. controlling vthe blanket heatv energy; it I is connected to .an alternatingcurrent source so that half-wave impulses arexsupplled to the control circuit. The amount of currentsupplied b t e valve to; the contro1-vcircuit- 1savaried by means of a network whichcontrols the grid voltage of-theval=ve. This network comprlsesacapaoitor-an cl two paralleland reversely connected electric valves monnected across the alternating current (source. Connections are ,provicledfrom the capacitorto the cathode andag rid of-the valve which supplies currentto the blanket jcontrol circuit. One 'of the' reversely cOnnectedvalveslsa grid-controlled valve, andvariation of its igrid voltage in turn varies the grid voltage of the-valve in (the control circuit. Means are provided "-for generating a controlling voltage which is-dpen dent upon the temperature-of the blanket. This controlling voltage is appliedto the grid of thereversly connected control valve, which thenoper- Iatesto control the valve in the blanket control circuit to cause it to control the blanket' -heat energy so as to operate the blanket at a selected temperature, The temperature held is selected lay-adjustable means in the means "for generating the controlling voltage.

'The controlling voltage preferably will he gjeneratedby meansof a Wheatstone bridge, which has one resistance leg' that responds "tolthefbla'nket "temperature and the resistance of which varies with temperature variations, anti another leg having a resistance which is adjustable. The bridge functions to'compare the resfstanc'esfof these ttvo legs and in doing 'soit geher'altes'the controlling voltage for then'etwork Whlch"'co'l1"- trols thevalve'in the blanket control circuit. The temperature setting-is effected by adjustlng'the adjustableresistance'of' the Other l'ek"'of the blld'gi riiigto"the 'd'rawmg, this invntion'has "been she'wmn one arm-as a rtime-amass electrican flieatjed b'lan a provided with a flexible lilanket o'dy "I to Which is aiziplie' d Heatin means 2 con g of a'p'air or nexiore resistance e16- men n ii'ne'ctel ogether inparallel and ehergmetli m asiiitable source of alternating current supgn '15 the biiiposlt" sides 'of which are 'c'oilhtil "G0 the blanket terminals 6 and. "I by rate s or eonuudtorsafa dte. shown, the

"of: cofivo'lu oiis covering "the respective halves -of "the blanket, ass own in 2, -It Will beunder- 'Efdbd that thefblafikt body Will be Provided with bl Chair-111515 (h OtTSh dWn) ih vfl-lilchithe ren'ce coriil'uctor's 3.2166 4 are threaded. Preferamy a' jblanketl bo'cly such as described" and i'c'l'ali hedj in'fthei United States patent to I O. 'r'irdce'rg No. 2 ,203 3918, date'i 'Juh'e 11, -1940; will be use I Order to "control"theenergization of the heating meansiso as-to'cyc'le theheating' means between erie- "ed and deener'giz'eclconcitions to hbld' a-"s'tibstantia'lly uniform" teinperature ;in the blanket, and also-so as to prevent overheating in; anf'p'a'it of the blanket; I provide a f ee ler lflilltlhiflhifih iiiferablyis the form Of a 'filarrierit, which. also is 'threadedfthrough suitable c haiine'rsrnm"snowm "oi-endedroritinthemesleeway- This element, as sh wn; 'isalso rerm'eq' ambs" l'urality of onventions" so that it th'ldlflghdtit th bla'hk t af'ea.

I'lils'f'eeler element TI is made of a'resista'nce l'fifitflbjl WI'ilh"VafiS' wi'd ely with t filplatlll changes. I prefer to use a material Whose resistaxncesincrases'raprdiy with increases inthe t'llfip el'afii. iIt 'li lay b' 'fdri'h'd of any Suitable material thistht acter, such'as nickel, are

65 m-551s they of nickel.

of the blanket together with "the control Suitable means are provided for controlling the energization of the heating means 2 responsively to changes in the resistance of the feeler circuit I l as the blanket temperature varies. This means comprises a Wheatstone bridge l2 having four resistance legs. One of these legs has a resistance l3 of fixed value, a second has an adjustable resistance l4, this resistance having an adjustable sliding contact I5, and a third leg has a fixed resistance H5. The fourth leg of this bridge is defined by the feeler resistance As shown, one terminal of the resistance H is connected to the terminal I! of the bridge which terminal joins it to one end of the leg I3. The other terminal of the ieeler circuit II is connected to the bridge terminal I8 which connects it to the leg I6, and this log in turn is connected to the leg M by a terminal l9, and this leg is connected to the leg |3 by a bridge terminal 20.

The bridge is electrically supplied from the alternating current source 5, the two conductors of which, as shown, are connected to the bridge terminals l8 and 20. A fixed resistance 2| is inserted in the upper conductor 5 which functions merely to drop the voltage across the terminals I8 and 20 to a desired value.

The bridge I2 functions to compare the magnitudes of the resistances II and I4. The resistance I4 is adjustable to set the blanket temperature. If the blanket temperature is greater than the temperature set on resistance I4, then the voltage across bridge terminals I1 and I!) will be such that the relay l will be deenergized, whereas if the blanket temperature is below the desired temperature the resistance in feeler circuit I will be lower than formerly and cause the voltage across points l1 and I9 to be such as to effect operation of the relay Ill to close and thereby reenergize the blanket heater. The nature of the voltage, therefore, across the bridge terminals I1 and I9 is an indication of the relationship between the magnitudes of the resistances II and I4.

The winding Illa of the relay I0 is controlled directly by means of an electric valve 22 which has an anode-cathode conducting path connected across the supply conductors and in series with the winding Illa. Although the valve 22 may be of any suitable type, it is preferably of the thyratron type having an anode, a cathode, and

a control grid and into the envelope of which a small quantity of an inert gas, such as mercury vapor or argon, is introduced. The presence of this gas within the envelope converts the usual pure electronic discharge into an arc stream, so that the valve becomes a grid-controlled arc rectiller. The grid has control only of the starting of the discharge. However, by varying the firing point, i. e., the time in the positive half-cycle of the anode voltage at which the grid voltage attains the critical value necessary to initiate current flow in the anode-cathode circuit, the average value of the current which flows in the output circuit can be varied. If the firing point occurs at or near the beginning of the positive halfcycle of anode voltage, maximum current will flow in the output circuit. If the firing occurs at the 180 degree point, the current flow will be a minimum or zero. For intermediate firing points the output current will have corresponding intermediate values.

As shown, the valve 22 has an anode 23, a cathode 24, and a control grid 25. The cathode is connected to the upper conductor of supply source 5 by conductors 26 and 21, while the anode 23 is connected in series with winding "la, and with the opposite side of supply source 5 through conductors 28 and 29. A filtering capacitor 284; is connected across the winding Illa.

For the purpose of varying the firing point of the valve 22 in each half-cycle of anode voltage, a network is provided which comprises two electric valves 30 and 3| and a capacitor 32. The upper terminal 33 of this capacitor is connected to the upper conductor of the supply source 5 by conductors 34, and 26, and 21, while the lower terminal 35 is connected through fixed resistor 36 and protective resistor 31 to the grid 25 of valve 22. The resistor 36 is connected in series with capacitor 31a across terminals 33 and 35 of capacitor. 32 for the purpose of obtaining I. fixed phase shift of the voltage appearing across the capacitor 32. The capacitor terminal 35 is also connected through the fixed resistor 38, the valve 3| and the conductors 39, 28 and 23 with the lowerconductor of supply source 5. Thus, the capacitor 32 is connected across the cathode 24 and the grid 25 of valve 22 so that any voltage across the capacitor will be applied across them modified as to phase or magnitude by resistor 36 or capacitor 31a.

Preferably, the valve 3| will be a trlode valve, having an anode 48, a cathode 4| and a control grid 42, the cathode being connected to the capacitor terminal 35 and the anode with the lower supply conductor 5, as shown. And preferably, the valve 30 will be similar to the valve 3|, having an anode 43, a cathode 44 and a control grid 45. This valve, as shown, has its anode 43 connected through the resistor 38 to capacitor terminal 35 and also through fixed resistor 46 to the grid 42 of valve 3|. The resistor 38, as shown, is connected across the grid and cathode of the valve 3| and is included in the anode circuit of valve 30 so that a voltage drop proportional to the anode current of valve 30 is produced across its terminals. A capacitor 41 connected in parallel with resistor 38 is charged by this voltage drop and applies a bias voltage to the grid of valve II which renders this increasingly negative as the current transmitted by valve 3| increases.

It will be observed that the valve 30 is connected in parallel with the valve 3|, and is reversely connected with respect thereto, 1. e., its anode 43 is connected to capacitor terminal 35 while the cathode 4| of valve 3| is connected to this terminal, and its cathode 44 is connected through the bridge I2 with the lower conductor of supply source 5, while the anode 48 of valve II is connected to this conductor.

Owing to the reverse connection of the two valves 3|] and 3|, both halves of the alternating voltage wave of the source 5 are applied to the capacitor 32 and thus the capacitor is alternately charged with voltages of opposite polarity. Thus, during the half-cycle in which the valve 3| conducts, the voltage of the terminal 35 is positive, and during the succeeding half-cycle in which the valve 3|] conducts, the capacitor is discharged and recharged to the opposite polarity, so that the terminal 35 has a negative voltage. If valves 30 and 3| conduct equal amounts, the voltage across the capacitor 32 is an alternating voltage having no direct current component. This 9.1- ternating voltage will lag the anode voltage of valve 22 by approximately degrees if the resistance of capacitor 32 is small compared to the equivalent resistance of the valves 3|! and 3|. However, if the amounts of current conducted by the two reversely connected control awn-cm valves are unequal; the altemating voltage across capacitor 32 will have a direct cm'rent c'omponent, the polarity-of which'depends 'upon'which of the two oppositelydirected our-rentsu-is the greater and the magnitude "depends upon the difference in theamountsuofthe two currents.

Thus, if the valve 31 conducts more current than does the valve the-polarity"Of the net: direct current component across capacitor 32 I will fibe 22' is connectedto the terminal" 35-, the effect of varying the direct-current component of the voltageacr'oss capacitor 32 1s to vary the firing point of the valve 22. '-as thedireotcurrent component increases in a direction to make terminal 35 less negative, the firing point ofvalve 22 is advanced and the amount or curren'ts'up plied by valve 22'to the winding Ma is correspondingly increased. -"Conversely, as *the direct current component is varied in adlrection'to make-terminal 35 more negative, the firingpoint ofvalve 22 is retardedand-'theamountof current suppliedto the winding l fla *iscorrespondingly decreased; i

The amount of current conducted by the-valve is controlledby the difference in potential across the bridge terminals I1 and I9 which volt age;"as'pointed out previously, depends upon the relative values of the resistances in the feeler circuit II and ofthe resistance l4. As shown,

the grid-45 'of the. valvem30j'isw connected to the bridge terminal 19 throughzarresistor' 48 and capacitor, while the cathode of this valve is connected to 'thebridge terminal 11. Thus, the bridge 12 in measurin the diiferences in the magnitudes of the resistances H and I4 applies a controlling voltage tothe grid cathode circuit ofthevalve 30. I

.The filaments of the tubes 22; "30 and are energized from the alternating current supply source 5 through a suitable transformer 50, the primary of which is connected across the conduct-ors of the source 5 and the secondary of which is connected to the filaments, as shown.

Preferably the relay [0, the bridge l2, and the controlling network described above will all be mounted in a suitable casing 5|, the casing being connected with the blanket through a cable 52 which houses the conductors 8 and 9 and the two conductors connecting the feeler II with the bridge terminals I! and i8. And connecting the casing with a suitable source of supply is a twin conductor cord 53 having the usual twin supply plug 54.

In the operation of the electric blanket, it will be understood that when the blanket is connected to the supply source 5 that the blanket body I will be relatively cool and, of course, so with the feeler circuit ll. Under these conditions, the voltage between the terminals I1 and I9 will be sufficiently negative to cause valve 30 to conduct less current than valve 3| and thereby make the voltage across capacitor terminals 33 and to become more positive which will advance the firing point of valve 22 thereby causing it to pass more current and thereby energize the relay In to close. This, of course, energizes the heating means 2 of the blanket. As the heatin means continues to heat, the temperature of the blanket body I will increase and so,

of course, will that of the feeler resistance ll.

reslstance onthe remen-circuit l l therefore, increases. --'When= iine temp'eratureot the blaniret attains the temperature set by contact 5- adf resistance H thevoltage -between= terrninals i8 an'd' l l 'wiil' 'increase-in apositive-sense causingv valve 30 to c'onduct more than v'al-ve thereby causing the voltage operating across capaciter terminals 33 and -35 tobecome more negative and thereby retarding the firing point of val-we aw-causing a decrease in current passed through valve 22 and thereby deenergizing relay Hltoper mit it to open an'd shut 'oif the heatto -blm'iliet body l'. Following this, the blanket temperature will iall and so will the resistanceiof theleeler circuit lil' unt'il it'reaches the value 'set by wa ta'ct ii'o'n resistor HI at which point-*the' rehy 10 is again energized in the manner described above "to v reapply heat to the blanket. "In this way; the system cycles the heatingmeans "on" =and d fi -to "hold -a *substantially constanttemperature in the blanket body I.

Ems-temperature may *be" varied "by adjusting the contactl5-to ad just'the effective reslstance of the resistor M. 'When this contact is moved 'in order to 'decrease :theamount of the-resistance connected in the bridge, this-will cause-the blanket temperature to be controlled-at a higher' -value. This -is becausethe resistance of ieelercircui't H 'm'ust 'attain a highervalue than before in order to cause a correct voltage to appear-across tennin'al's N and 19 to 'operate the relay 1 0' to open the heating" circuit. Conversely, if the contact 5 l d-is adjusted tofincrease the effective resistance erresistorl l then the blanket is held at a lowertemperatu're.

Itwi'll be understood that if the blan'ket :becdvered or fdlde-d accidentally so that apart thereof tends 'to elevate' to a dangerously high temperature the resistance of the feeler circuitas awh'ole 'will be increased which will operate inthe manner described above to cause the relay l fl te deen ergize the heater. I

' mso'lit will be understoodithat if the fe'eler cincuit lil shouldibe opened, then the relayx l l will be opened because in efiect the resistor l i becomes infinite.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Lett-ers Patent of the United States is:

1. An electric blanket and the like comprising a blanket body, heating means for said body, means for controlling said heating mean including a control circuit therefor controlling said heating means in accordance with the current in said circuit, a source of alternating current voltage, means for supplying half -wave unidirectional current to said control circuit comprising a controlling electric valve provided with an anode, a cathode and a control grid, and having its anodecathode path included in .a circuit with said source and said control circuit, means for supplying to said grid a voltage having a periodically varying component and a direct component comprising a capacitor having connections to said grid and cathode and a pair of reversely connected electric valves connected in circuit with said capacitor across said source, one of said reversely connected valves having an anode, a cathode and a control grid, and means for supplying to the grid and cathode of said reversely connected valve a voltage responsive to the temperature variations of the blanket body so as to supply a voltage to the grid of said controlling electric valve to control the current in said control circuit in order to hold a substantially constant temperature.

2. An electric blanket and the like comprising a blanket body, heating means for said body, means for controlling said heating means including a control circuit therefor controlling said heating means in accordance with the current in said circuit, a source of alternating current voltage, means for supplying half-wave unidirectional current to said control circuit comprising a controlling electric valve provided with a cathode, a

control grid, and an anode connected to said control circuit and one side of said source of voltage, and said cathode connected to the other side of said volta e source, and means for supplying to said grid a periodically varying voltage having a direct-current component comprising a capacitor having one terminal connected to said grid and the other terminal to said cathode, and two reversely connected electric valves connected in circuit with said capacitor across said source, one of said reversely connected valves being a triode valve provided with an anode, a cathode and a control grid, a resistance in said blanket having a resistance which varies widely with temperature changes, an external resistance, means interconnecting said resistances for comparing the magnitudes thereof and for generating a controlling voltage which varies in magnitude with the differ ence in said resistance magnitudes, and means for applying said voltage to said grid and cathode of said triode valve to control the firing of said controlling valve and thereby control the current in said circuit.

3. An electric blanket and the like comprising a. blanket body, heating means for said body, means for controlling said heating means including a control circuit therefor controlling said heating means in accordance with the current in said circuit, a source of alternating current voltage, means for supplying half-wave unidirectional current to said control circuit comprising a controlling electric valve provided with an anode, a cathode and a control grid, and having its anodecathode path included in a circuit with said source and said control circuit, means for supplying to said grid a voltage having a periodically varying component and a direct component comprising a capacitor having connections to said grid and cathode and a pair of reversely connected electric valves connected in circuit with said capacitor across said source, one of said reversely connected valves having an anode, a cathode and a control grid, a Wheatstone bridge having one leg defined by a ieeler resistance element which is distributed through said blanket body and whose resistance varies widely with temperature change, and a second resistance exterior of said blanket body, said bridge having a voltage across its two output terminals which voltage is a measure of the difference in the magnitudes of said feeler resistance and said external resistance, and connections between said bridge terminals and the grid and cathode of said reversely connected valve for controlling the firing thereof in accordance with said voltage whereby a voltage is supplied to the grid of said controlling electric valve to control the current in said control circuit in order to hold a substantially constant temperature in said blanket body.

HARRY W. A. CHALBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,979,467 Hellmuth Nov, 6, 1934 2,086,966 Shrader July 13, 1937 2,098,650 Stein Nov. 9, 1937 2,198,462 Donle et a1 Feb. 6, 1940 2.203918 Moberg June 11, 1940 

